Magnetic sensor with squid and having superconducting coils formed on sapphire substrate

Abstract

This magnetic sensor comprises a flux transformer 2 having a superconducting thin film 2 f formed on a sapphire substrate 2 s , and a SQUID 1 disposed on the flux transformer 2 opposite thereto. In this magnetic sensor, since the sapphire substrate 2 s , which can be obtained in a large size, is used for the flux transformer 2 , even when the SQUID 1 is made smaller, the magnetic flux introduced from the flux transformer 2 into the SQUID 1 can be enhanced so as to increase the effective magnetic flux capturing area, whereby the detecting performance is improved, while the manufacturing cost can be reduced due to the smaller size of the SQUID 1.

What is claimed is:  
     
       1. A magnetic sensor comprising: 
       a flux transformer having two coils electromagnetically connected to each other, said coils being formed on a first substrate; and  
       a SQUID having an annular part opposite to said flux transformer, said annular part facing one of said coils of said flux transformer, said annular part being formed on a second substrate, a predetermined portion of said annular part forming a Josephson junction by covering a step edge which traverses thereunder,  
       wherein  
       one of said coils is larger than the other one of said coils;  
       the larger one of said coils is larger than said annular part;  
       the smaller one of said coils faces said annular part;  
       an outside diameter of said annular part is not greater than 5 mm;  
       both of said coils and said annular part are made of a superconducting material comprised of Ho, Ba, Cu and O;  
       said first substrate is comprised of a sapphire substrate and a cerium oxide layer is interposed between said sapphire substrate and said coils; and  
       said second substrate is comprised of Sr, Ti and O.  
     
     
       2. A magnetic sensor according to claim  1 , wherein 
       said annular part has a slit cut toward a position between a predetermined outer edge point and a predetermined inner edge point of said annular part from a point different from said predetermined outer edge point in said outer edge;  
       said Josephson junction traverses between said predetermined inner edge point side of a ridge defining said slit and an inner edge of said annular part; and  
       said larger one of said coils acquires a magnetic flux of a subject to be detected.  
     
     
       3. A magnetic sensor according to claim  2 , wherein said smaller of said coils faces said annular part of said SQUID and covers an entire region of said slit.